Implement method .cycle() that repeats an iterator endlessly
Implement Clone for simple iterators (without closures), including VecIterator.
> The theory is simple, the immutable iterators simply hold state
> variables (indicies or pointers) into frozen containers. We can freely
> clone these iterators, just like we can clone borrowed pointers.
The theory is simple, the immutable iterators simply hold state
variables (indicies or pointers) into frozen containers. We can freely
clone these iterators, just like we can clone borrowed pointers.
VecIterator needs a manual impl to handle the lifetime struct member.
Some notes about the commits.
Exit code propagation commits:
* ```Reimplement unwrap()``` has the same old code from ```arc::unwrap``` ported to use modern atomic types and finally (it's considerably nicer this way)
* ```Add try_unwrap()``` has some new slightly-tricky (but pretty simple) concurrency primitive code
* ```Add KillHandle``` and ```Add kill::Death``` are the bulk of the logic.
Task killing commits:
* ```Implement KillHandle::kill() and friends```, ```Do a task-killed check```, and ```Add BlockedTask``` implement the killing logic;
* ```Change the HOF context switchers``` turns said logic on
Linked failure commits:
* ```Replace *rust_task ptrs``` adapts the taskgroup code to work for both runtimes
* ```Enable taskgroup code``` does what it says on the tin.
r? @brson
r? @brson `rustpkg build`, if executed in a package source directory inside
a workspace, will now build that package. By "inside a workspace"
I mean that the parent directory has to be called `src`, and rustpkg
will create a `build` directory in .. if there isn't already one.
Same goes for `rustpkg install` and `rustpkg clean`.
For the time being, `rustpkg build` (etc.) will still error out if
you run it inside a directory whose parent isn't called `src`.
I'm not sure whether or not it's desirable to have it do something
in a non-workspace directory.
